the first?
i'd say pokemon, yu gi oh, or digimon would have been my "first"

what i would count as my first anime would be dragon ball. first series i actually watched and finished would be Eureka 7.
actually getting into anime and watching it regularly would have been summer 2013, starting with SAO and when it first started airing.

Technically, the first anime i watched was Pokemon as a child, but i never watched it properly, it was kind of just something i watched when there was nothing else on and i got the chance to put it on. As an adult, the first anime i watched was Dragon ball